This invention relates to techniques concerning measurement of a test chart used to correct output colors of a color output apparatus such as color printer or color copier and correction of the output colors using a color measurement result.
Generally, output colors of a color output apparatus such color printer or color copier slightly vary due to environmental factors such as temperature and humidity and with the lapse of time even within one day. Particularly, the output colors are corrected once or more within one day in a color output apparatus used as a small-sized printing apparatus. A test chart in which a plurality of color samples having different tones and different densities are arrayed is used for the correction of the output colors. Specified control information is sent from, for example, a personal computer to a color output apparatus as an, object to be corrected, the color output apparatus is caused to output a test chart used for the correction, and output colors are corrected based on differences between the measurement results and color values the respective color samples should have.
It takes a long time if the colors of the test chart are measured for each color sample using a usual manually operable colorimeter. Accordingly, linear scan type colorimeters in which a single color measuring sensor is moved in one direction and two-dimensional scan type colorimeters in which this color measuring sensor is moved in vertical and horizontal directions have been used.
For the colorimeter of the former type, a strip-shaped test chart in which color samples having different tones are arranged in a plurality of rows and densities thereof gradually change between the rows as shown in FIG. 16 is used. Color measurement data of the respective color samples are obtained by causing the color measuring sensor to longitudinally scan the test chart.
On the other hand, for the calorimeter of the latter type, a test chart in which a much greater number of color samples than the test chart for the linear scan type colorimeter are two-dimensionally arrayed as shown in FIG. 17. Color measurement data of the respective color samples are obtained by causing the color measuring sensor to longitudinally and laterally scan the test chart.
Since the conventional linear scan type colorimeter needs to scan each row of the test chart for the color measurement, a manual operation to change the row to be scanned is necessary. This results in a poor operability. On the other hand, the two-dimensional scan type colorimeter does not require the row to be scanned to be manually changed unlike the conventional linear scan type colorimeter and, accordingly, measurement can be completely automated. Thus, a test chart in which a larger number of color samples are two-dimensionally arrayed can be used. However, such a test chart is expensive to manufacture and is disadvantageous in terms of costs.
Further, since either colorimeter is of the scan type, the more the color samples, the longer time is required for the color measurement. Further, since the color measuring sensor is driven to scan, scanning precision and a dimensional reproducibility of the test chart need to be considered in order to precisely extract adjacent color samples. Such considerations lead to increased costs.